SSTO Design - Critical Fuel

[ThePULSAR]

The Problem with SSTO is the Delta-Vee,I always use up liquid fuel before I orbit Kerbin.

Any good design?

Edited November 5, 2015 by ThePULSAR

[DCWarHound]

Post some pics of it.

You probably have too little fuel in the first place.

You need a good balance of LF+O, LF, TWR and lift to make an SSTO.

[Starhawk]

Hey ThePULSAR, take a look at the K Prize thread in challenges. There are a lot of great designs there. You only want to look at ones made after 1.0 came out.

Happy landings!

[Brainlord Mesomorph]

I often stock a small spaceplane with ALL LFO.

Sure you're carrying extra oxidizer, but you burn so little jet fuel before you need LFO, its not worth LF only tanks. (that's how I won the k-prize -- WOW one year ago today!)

Edited November 5, 2015 by Brainlord Mesomorph

[ThePULSAR]

Thank you for the suggestions!

[SpaceplaneAddict]

Well, I can say that RAPIERS are gas guzzlers in both ways. Often, they need a full jet fuel tank JUST for Airbreathing mode.

-SPAddict

[cantab]

Things I would look at:

Are you getting a good speed on the jets. I'd say aim for 1300-1400 m/s before you switch to rocket power. It took me some practice to get the hang of accelerating high, fast, and level - it's very easy to pick up too much climb rate at too low a speed.

When the rockets flame out, do you have excess oxidiser? If so that's dead weight costing you delta-V, so go back to the SPH and remove some oxidizer from the tanks. Usually what I then do is switch to rockets when I've burnt off enough fuel that the remaining fuel:ox ratio is right, ensuring I'm not hauling useless excess propellant to orbit. (Keeping a small amount of excess fuel for power when landing may be wanted)

If that still doesn't work, then you probably need more fuel tanks. That said, a single-seater RAPIER-powered spaceplane can make orbit with just one FL-T800 tank. It's when you want to carry heavier loads, or have delta-V in LKO to go places, that the fuel requirements climb.

[Val]

*shameless self plug*

You're welcome to look for inspiration in my [thread=136017]builder thread[/thread] or my KerbalX hangar.

All the downloadable craft come with instructions on how to get to orbit.

Edited November 5, 2015 by Val
Grammar

[panzer1b]

I often stock a small spaceplane with ALL LFO.

Sure you're carrying extra oxidizer, but you burn so little jet fuel before you need LFO, its not worth LF only tanks. (that's how I won the k-prize -- WOW one year ago today!)

This is nolonger the case. 1.0 made jet engines eat 10 or so times the fuel, most of the time, you will eat 1/4 or so of the total fuel mass with just jets during ascent.

Anyways, as for the question, ive found the best combo to be ~4000 LF (powered jet in jet mode and nuke in space), with ~100-200 OX to run the rapier in rocket mode (nuke alone has trouble lifting 30 tons into orbit withotu the rapier in rocket mode). The engine layout is one nuke and 1 rapier, and this craft (provided you dont bring 2 tons of weapons with you), can get over 7000 dV in LKO (enough to land on laythe, bop, and pol in one go, and return to kerbin without any refueling).

Anyways, for a very basic SSTO (only gets to LKO with ~2 tons of cargo), is a (from front to back):

Air intake (shock is best but the other 2 will work technically), mk1 inline cockpit, mk1-mk2 adaptor, the shorter of the 2 mk2 bomb bays, mk2-mk1 adaptor, rapier engine. Then add around 2-3 lift rating total of wings, and all the usual gear your need (wheels, solars/batteries/RTGs, RCS system and docking ports if you actually want to dock this, ect). This is a proven and reliable design, extermely simple, and low on part count/lag. Also, for fuel, drain half the oxy total from both tanks, so you should have 360 total LF, and ~220 OX left.

For longer ranges, you will need ALOT more LFO in general, and that means scale up the fuel tanks. For conventional designs, one rapier can lift ~15 tons, and once in space TWR is not that critical, making nukes a very good interplanetary engine that doesnt actually use OX at all allowing some pure jet+nuke hybrids (ions moreso but im not that patient and they have greater limitations especially when you are trying to burn to outer planets where you are on the dark side of planet making solar panels worthless). Anyways, just check out the forum, there are many great designs for a variety of tasks, and there are even soem thready about specifics in terms of stuiff like best fuel ratios for different payloads, wing area, ect.

Edited November 5, 2015 by panzer1b

[Brainlord Mesomorph]

This is nolonger the case. 1.0 made jet engines eat 10 or so times the fuel, most of the time, you will eat 1/4 or so of the total fuel mass with just jets during ascent.

thanks for the correction. I've haven't built any small planes in 1.0, just giant ones. I did notice they seemed to burn alot of fuel, but I thought it was because of their size.

[Gojira1000]

I'm trying to recall the basic Bee layout I use while at work. As I recall, MkI inline cockpit, three shock cones, 2 rapiers, 1x 2.5 ton LF-only tank, 6x 2.5-ton LFO tanks and orbit as desired up to 100km with plenty for re-entry and powered landings. I'm sure oxidizer can be tweaked on that.

[AeroGav]

A lot of my designs have a 5:1 ratio of liquid fuel to oxidizer, when you click on the resources tab to look at the totals. That is because I generally use 2 RAPIER and 1 nuke for propulsion. At the point where I switch over to closed cycle mode, 40% of the liquid fuel is gone. The next 20% gets burned with the oxidizer in the RAPIERS, and the rest is used by the LV-N to complete orbital insertion and for interplanetary travel.

Incidentally, when i was trying to optimise my flight profile i discovered that the initial subsonic fuel uses very little fuel however it is flown. However, the acceleration to mach 3 and climb to 20k is another matter. When your Rapiers get up on the power band and start boosting like crazy, it doesn't come for free i've found.

Above 20km, their thrust and fuel consumption die off together. However, be aware that holding the nose down to try squeeze out that last 100 or 200 m/sec from air breathing node can get costly. Each design has a different natural top speed. I built an IRSU mining ship for Minmus, and wasted a ton by trying to force it to 1500/1600 m/s. Eventually realised this design cannot go above 1400 in level flight.

My usual rides have quite generous wing area and only moderate thrust-weight ratio, but are pretty clean aerodynamically and are intended for bringing a small scientific payload a long way, rather than a large mass barely to orbit. I